Antimicrobial resistance

Antimicrobial resistance is the capability that a microbial pathogen (for example, a bacterium, virus, parasite, or fungus) acquires to counteract an inhibitory molecule or compound that was formerly effective in killing it or preventing its growth. In general, antimicrobial agents are biosynthetically or synthetically produced chemical compounds that can selectively destroy harmful microbes or suppress their growth. Depending on the type of microbe that is attacked, these compounds can be classified as antibacterial, antifungal, antiparasitic, and antiviral agents, and they include many important drugs and antibiotics (such as penicillin, tetracycline, and neomycin). Because of major changes in human demographics and behavior, and the sometimes reckless past overuse of antimicrobial compounds, the problem of antimicrobial-resistant pathogens—and the concomitant resurgence of bacterial and viral diseases in particular—is becoming a global health concern. See also: Antibiotic; Antimicrobial agents; Bacteria; Clinical microbiology; Fungi; Microbiology; Parasitology; Pathogen; Penicillin; Public health; Virus

Since the 1940s, antimicrobial drugs have been used effectively to prevent and halt the spread of infectious diseases. However, many of these antimicrobial agents, especially antibiotics, have lost their effectiveness because they have been overused and misused for many years, allowing the infectious pathogens to adapt and evolve into drug-resistant organisms. According to the U.S. Centers for Disease Control and Prevention, about half of all the antibiotic use in humans and animals is inappropriate and unnecessary. In addition, other factors have contributed to the worldwide emergence of antimicrobial resistance, including the increasingly global nature of the food supply; the modern mobility of people, animals, and microbes, which enables them to travel great distances in short amounts of time; disruptions to ecosystems, typically resulting from economic development and land-use changes; and the large concentrations of children in day-care centers, especially in economically developed countries. See also: Drug resistance; Infectious disease

One example of the growing threat posed by antimicrobial resistance can be seen in patients affected by methicillin-resistant Staphylococcus aureus (MRSA). Normally, the bacterium S. aureus coexists peacefully with its host (in a process called colonization), living on the skin, in the nasal passages, or in the intestinal tract without causing problems. In certain situations, though, the penetration of host barriers by S. aureus can lead to very serious conditions, including skin and wound infections, pneumonia, and bloodstream infections that can cause sepsis and death, which can only be treated by effective antimicrobial therapy. In addition, S. aureus is among the most common causes of nosocomial (hospital-acquired) infections. Unfortunately, S. aureus has adapted and become resistant to antimicrobials in the beta-lactam family (which includes methicillin, penicillin, and cephalosporin), thereby limiting treatment options. See also: Hospital infections; Human susceptibility to Staphylococcus aureus; Methicillin-resistant Staphylococcus aureus in the horse; Staphylococcus

Moving forward, a multifaceted worldwide effort will be required to control antimicrobial resistance among disease-causing microorganisms. Decreasing the use of antibiotics is a first necessary step to combat antimicrobial resistance. Moratoriums on the use of specific antibiotics may allow vulnerability to them to creep back slowly into pathogen populations. Because bacteria and other microbes have shown a remarkable ability to adapt to the intense selection pressures of antimicrobial therapy, newer classes of antibiotics and antimicrobial agents will also have to be developed. Other efforts are focusing on genetic aspects of the problem, applying the use of genome editing tools to kill resistant microbes or to eradicate the genes responsible for the antimicrobial resistance. See also: Treating superbugs: CRISPR-genome editing

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